Rename factory methods creating LBModelRepository

Rename factory methods in `LBRESTAdapter`  to
  `repositoryWithModelName:(NSString *)name`
  `repositoryWithModelClass:(Class)type`

As discussed in strongloop/loopback-ios-getting-started#3.

This PR incorporates changes from strongloop/strong-remoting-clients#5.

/to: @Schoonology please review